1. Field of the Invention
The present invention relates to a vehicle navigation device that allows a driver to easily reach a predetermined destination by guiding the vehicle to the destination. More particularly, the present invention relates to a suitable navigation device having the function of scrolling a map image by a user operation.
2. Description of the Related Art
In general, in a navigation device for guiding a vehicle, for example, a self-contained navigation sensor and a global positioning system (GPS) receiver are used to detect the present position of the vehicle. Then, map data of an area near the detected present position is read out from a recording medium (such as a DVD), a map image is plotted on a display device, and a vehicle position mark is superimposed and plotted on a predetermined position of the map image. In accordance with changes in the present position of the vehicle due to the movement of the vehicle, the vehicle position mark is moved on a screen, or the vehicle position mark is fixed at a predetermined position on the screen and an area of a map image near the predetermined position is scrolled, so that the user can know the present position of the vehicle at a glance.
Almost all recent navigation devices have a route guide function that allows a driver to easily drive to a predetermined destination without taking a wrong route. In the route guide function, using map data, the least expensive route connecting the place of departure to the destination is automatically searched as a result of simulation by breadth-first search (BFS) or a Dijkstra method. The searched guide route is plotted heavily with a color that is different from the other roads on a map screen while driving. When the vehicle moves within a certain distance of a guide intersection on the guide route, the driver is guided to the intersection by being informed of the direction of travel by a voice or by an arrow indicating the direction of travel after enlarging and displaying a guide image of the intersection.
In this type of navigation device, it is possible for the user to scroll a map displayed on the screen in any direction by displaying a cursor on a navigation screen by operating an operation section, such as a touch panel or a remote controller. In other words, when, with the cursor being fixedly displayed at a predetermined location on the screen, the user operates the operation section to move the cursor, the map on the screen is scrolled in accordance with the movement of the cursor.
Such a screen scrolling operation using a cursor is carried out, for example, to search for a predetermined point of interest on the map screen or to give an instruction to the navigation device body for using a point where the cursor is located for various functions (such as for setting a destination or a route along the way by route searching or for indicating the present position). The screen scrolling is often carried out when the user is trying to ascertain beforehand the road or roads ahead while driving.
However, when the driver performs screen scrolling while driving, the driver cannot pay full attention to his/her driving because he or she must perform the screen scrolling while steadily looking at the map screen. As one means for solving this problem, the function of automatic scrolling along a set guide route is generally used. As another means for solving this problem is disclosed in Japanese Unexamined Patent Application Publication No. 8-190343, in which the function of allowing scrolling of a map along a route is accomplished by selecting a road scroll mode and by operating a joystick.
In general, a driver tends to drive his/her vehicle based on the location of a nearby main road. For example, the driver tends to think of turning to the right at a certain corner because a certain street is situated ahead. For this reason, it is very important for the driver to safely and reliably find an intersection that joins a main road by screen scrolling even while driving.
However, the related function of screen scrolling along a guide route cannot be used when a guide route is not set. In addition, even if a guide route is set, screen scrolling is performed automatically along a set guide route, thereby making it impossible to confirm a main road that is not situated on the guide route.
In the related art disclosed in Japanese Unexamined Patent Application Publication No. 8-190343, because screen scrolling is performed along a road, the user can relatively easily operate the cursor when a road is bent. However, in order to ascertain a predetermined main road, it is nonetheless necessary to scroll a map on the screen while steadily looking at the map screen. Therefore, the driver still cannot pay full attention to his/her driving.